Electronic motor control circuit



ELECTRONIC MOTOR CONTROL CIRCUIT Filed April 17, 1951 2a-= 21 asINVENTOR Ilerngn 1? Ra'ab j ATTORNEY Patented Dec. 29, 1953 ELECTRONICMOTOR CONTROL CIRCUIT Herman P. Raab, Indianapolis, Ind., assignor toRadio Corporation of America, a corporation of Delaware ApplicationApril 17, 1951, Serial No. 221,384

4 Claims.

This invention relates generally to the control of electric motors andmore particularly to controlling the speed and/or angular displacementof alternating current motors.

Accurate control of the speed or angular displacement of an electricmotor is desirable in many applications, for example, the control ofguns, searchlights, directive radio antennas and the like. Indisplacement control systems it is usually desirable to control therelatively large mechanical power output of a motor in response to arelatively small input such as may be conveniently produced by amanually operable crank or an indicator. Direct current motors areparticularly adapted to such applications which require wide Variationof motor speed and motor torque. However, alternating current motors areless expensive and alternating current energy is usually more readilyavailable than is direct current energy. Thus, for reasons of economy,it is frequently desirable to employ an A.C. motor, although the controlcircuits may be more complex than those which would be required for aD.-C. motor.

Some previous control circuits for two-phase A.-C. motors apply fixedexcitation to one winding and vary the amplitude and polarity ofexcitation of the remaining Winding while maintaining a fixed phaserelation between the currents in the two windings. The instant inventionprovides novel means for controlling the speed and/or angulardisplacement of two-phase motors by varying the relative phases of thecurrents flowing through the phase windings.

It is an object of this invention to provide an improved means forcontrolling the speed and direction of rotation of an A.-C. servomotorin response to the magnitude and polarity of an applied alternatingpotential.

Another object of the invention is to provide an improved full waveservomotor control circuit for controlling simultaneously the loading oftwo windings of a reversible induction servomotor in response to thepolarity and magnitude of an applied control potential.

A further object of the invention is to provide an improved full waveservomotor control circuit for controlling a two-phase induction motorby varying the relative phases of the currents fiowing through the motorphase windings in response to the polarity and magnitude of an appliedcontrol signal.

According to a typical embodiment of the instant invention, there isdisclosed a circuit in which a thermionic triode, a thermionic diode,

and a blocking capacitor constitute a bilateral dissipative unit of highimpedance. Shunting this high impedance unit is a phasing capacitor towhich is serialiy connected one winding of a two-phase servomotor.Similar circuitry is connected to the second winding of the two-phaseservomotor. With no control signal applied to said units, which are bothnormally of high impedance, the motor windings are supplied withexcitation current t rough the identical phasing capacitors. Theexcitation currents of both windings are then in phase and hence notorque is produced. Application of a push-pull control signal to thesebilateral dissipative units, however, causes the impeoance of one of theunits to approach a low value. This shunts its associated phasingcapacitor and effectively shifts the phase of the excitation currentfiowing through the phase winding connected thereto. Hence, outputtorque is developed and the motor rotates, its direction of rotation andspeed being dependent upon the polarity and magnitude, respectively, ofthe control signal.

The invention will be described in greater detail with reference to theaccompanying drawing in which the single figure is a schematic circuitdiagram, according to the invention, of a control circuit for atwo-phase servomotor in which the speed and direction of rotation arecontrolled by respectively varying the magnitude and phase relation ofthe currents flowing in the two windings of the motor.

Referring to the drawing, a source of alternating potential, not shown,is connected to input terminals l and 3 terminating the primary winding5 of a transformer I having a secondary winding 9 coupled thereto. Oneend of the transformer secondary winding 9 is successively connected toone phase winding H of the two-phase motor, a D.-C. blocking capacitorl3, and to the anode electrode of an amplifier tube i5. The cathodeelectrode of the amplifier I5 is then returned to the remaining end ofthe transformer secondary 9. A diode tube I! is connected backto-baclwith the triode amplifier I 5; that is, the tubes are parallel connectedbut oppositely polarized. shunting the back-to-back connected triode l5and diode I l and the D.-C. blocking capacitor l3, is a phasingcapacitor l9. Similar circuitry connected to a second field winding H,one end of which is connected to the same end of the transformersecondary winding 9 as is the first field Winding l l, is designated byprimes. A center-tapped resistor 2|, which is connected between a biassupply 22 and the control electrodes of the 'triode amplifiers l and I5,and a pair of coupling capacitors 23 and 23' provide means for applyinga control signal from a pushpull signal source 25 to the motor controlcircuit.

When the circuit is in operation and no control signal is appliedthereto, the triode amplifiers l5 and I5 are. cutoli", and flow ofcurrent in diode tubes l'l, andfl'i': i'sfpreyented by lilggl zillgcapacitors l3 and I3, respectively.

The two-phase windings ll and H are then supplied with excitationcurrent through the identical phasing capacitors) and I9. Since thecurrents in the 'two notgr windings it and are in phase, 110 outwit; ideranged:

A push-pull control signal is applied to the control electrodes of thetriodes l5 and i5 and is of proper phase with respect tothe'line'potential so that one of the triodes, for Eg gampla l5 conductson positive half-cycles of the control -ignal thereby shuntingitsassociated phasin citor 13 by said conduction reducing the imenc of thhi cr sta er-e n t to a relatiyclylbw value, Sincethe phasing capacitoif9 is"shunted,'the current thra g'h the assojof'wmain illsefiectiyelyshiited in 1, "negatyelialf'cycles of the control signal theassociateddiode ll efiectiifely conf'lheblocls'ing capacitor l3 permitsno lQ-C. curre'ntto flow through the'moto'r'windin l I "sothe'uncontrolled diode current cannot eed hefcontrclledttiode current; Thusthe t ase'mbtorwindings' Hand ll are efiec- ,tiv it''dwith 'full waveenergy, and be pause o the shunting of the phasing capacitor A. controlsignal of the opposite instantaneous e are; th cn i siried mem 5' to ntits ass ciated phasing capacitor 19 so and of sister mafsilhstaritiallybe realized A for mmti rm'mbe'may be substituted for the triodesusedherein.

The motor control circuit thus disclosed is particularly ad antageouswhn'a number of separate se otors are used in a given "syst lt may 'b'ei'sen only one isolation i Re orme equ ed i er iiic d s thet sin esecondar W ndi f th tra er e Su ly a l lit o vo qto -f Whcti cl imed is:

4 weird circuit o a wo-ph se motor vies ai of fieldw i ss sa d ci c t gr es cc ic mean or c u es a fi s w if al rn t ng Poten ial to sa d i toW lie e! a reg eithsrgaie c tub s were !ie a in p et te r larit 'an iwit eac if i i -sin s; a acit re it sach a d W sin an ube air t Phasingcapacitor in parallel withea'ch oisaid tube pairs, and connection man ona second source of altihatiligpdtntial for couplil ig control signalsfrom'aiidse'cond's curce to an'electro'de of atube of ac'n'tr's idp rs'for shunting io'ne of said 4 phasing capacitors to load said motor topro duce rotation thereof.

2. A control circuit for a two-phase induction motor having a pair offield windings, said cir-' cuit comprising connection means for couplinga first source of alternating potential to said motor windings, a pairojithern ionic tubes parallel connected in'opposite polarity and serieswith each of said'fiel'd windings, a blocking" capacitor seriallyconnected with and intermediate each field winding and tube pairassociated therewith, a'phasing' capacitor connected in parallel witheach of said tube pairs and in series with each of said bloekicapacitors, connection means for a second so roe of alternatingpotential, and means for applying control signals from said secondsource 'in'push-pull relationship to an electrode ofone tube of each ofsaid tube pairs for shunting one of said phasing capacitors to load aidmqto ltq rod ce rotation thereo ce-"W 1 c c i itficr tw ip le e mete a na a o fi ld winqin l id c r i o nismg connection'means for coupling afirst source Q a erna n qt h ial' v a d m or wi di a! Pai b rm o tu e al concede in opposite polarity and in'series with each of sa fi ld widin s whisking ara e: ia connectod with and intermediate each fieldwindt ns n ube ai ass c a d he w th a Rhe ing capacitor in parallel witheach oisaid" tube pairs, and connection means tor a second s'our'ce o aterna in potenti for ou n cqii q sisnals from said second source toshunt one'oi s'aid phasing capacitors to load said motor to"itrotationthereoi. Abo' t l fl rt 'f fo a two-pha e i du tio motor hav apair of fi l wi n s. an ci cuit comprisinsfl nn t means or couplin afirst source oi alternating potential a said fibpr tt field windings, ablocking capacitor serially. conne t w th an inte mediate eac m tzint ea d ube p ir a cia'tld'therf. ith," a biasing capac to conne tetlo paralel h' "ffb said t pe pairs a d iiiseriesw tn s id blo kin capacit rs conec n m a s fo a of alternatin mental; d me" ing control signals fromsaid same in ast- 91in relationship to the triodes o'fsaid tube pairsload it new" pi et e carer teast" ie er eces it-2 e h l of his e setUNITED S'LATES Number Name Date 2,351,759 Grundn'iann June QUElQM2,351,760 Beets -g- Jjfiiao; i944 2473394 f p 'm F '1:

FOREIGN PATEN'IS Num er cliet a 5515, Ge man Ne -"5 ,93

OTHER REFE ENe-Es The Splat gystem, o YLNQ-l Mariell 1946, page 14,Solar Manufacturing-

